Magna Carta

IX Liberties of London, &c.

THE City of London shall have all the old Liberties and Customs [which it hath been used to have]. Moreover We will and grant, that all other Cities, Boroughs, Towns, and the Barons of the Five Ports, and all other Ports, shall have all their Liberties and free Customs.

https://www.legislation.gov.uk/aep/Edw1cc1929/25/9/section/IX

https://en.wikipedia.org/wiki/City_of_London_Corporation#cite_note-5